In the prior art charge-coupled devices (CCD) a limitation in their operation occurred because of radiation effects thereupon. A common effect observed in both surface and buried channel CCD's was the threshold voltage shifts caused by radiation-induced increases of positive oxide charge.
This oxide charging effect was the principal limiting factor in buried channel devices exposed to radiation, because it caused surface potential variations that decreased the device's full well signal charge capacity. When operated at initially set gate voltages, the device ceased to function in the buried channel mode at advanced levels of the increased oxide charge. Oxide charging effects, similarly, degrade the performance of the irradiated surface channel devices.
The present invention provides an easily integrable circuit that when incorporated with a CCD stabilizes the surface potential against oxide charging effects by regulating the applied gate voltage. Incorporating this circuit with the buried channel CCD, the complete integrated unit (i.e., circuit and CCD) is effectively radiation hardened over an extended range of operation. Similarly, using this circuit to regulate the gate potential of the surface channel CCD, the range of operation of the CCD is a radiation environment is extended. In addition, a small DC current level ("fat zero") must be included to control interface losses. This circuit aids in optimizing and stabilizing the efficient performance of charge-coupled devices.
It is noted that charge-coupled devices have many potential applications in electronic systems. These devices can be used for optical and infrared imaging systems, delay lines, and a variety of signal processing functions. If any system employing charge-coupled devices is to be used in a space or nuclear radiation environment this invention may be essential to the proper operation of the device. In nonradiation environments, the invention may improve the long life reliability of the circuit.